As shown in FIG. 1, a pixel point of a conventional liquid crystal display panel includes three sub-pixels including red, green and blue (RGB). Each sub-pixel has a total of 256 from 0 to 255 gray scale levels. Different colors are formed by combining different gray scales of the red, green and blue sub-pixels. Thus, represented by the RGB model, RGB (X, Y, Z) can represent various colors, wherein X is a gray scale level of the red sub-pixel, Y is a gray scale level of the green sub-pixel and Z is a gray scale level of the blue sub-pixel, 0≤X, Y, Z≤255. For example, red can be represented by RGB (255, 0, 0). RGB (X, Y, Z) is normalized to RGB (x, y, z), 0≤x, y, z≤1, wherein x is a normalized gray scale level of red sub-pixel, y is a normalized gray scale level of the green sub-pixel and z is a normalized gray scale level of the blue sub-pixel.
Since a red light, a green light and a blue light are overlapped to form a write light, people innovate an RGBW model by adding a white sub-pixel on a basis of the conventional three basic colors RGB. As shown in the drawing, for a single pixel, compared with the RGB, the RGBW has the white sub-pixel. However, a size of an entire pixel is not changed, so the sizes of the red, green and blue sub-pixels of the RGBW are smaller than these of the RGB. In fact, the sizes of the red, green and blue sub-pixels of the RGBW is a ¾ of the sizes of the red, green and blue sub-pixels of the RGB.
In the present RGBW model, the red, green and blue sub-pixels respectively generate the red, green and blue lights with the same quantity, which are replaced by a white light generated by the white sub-pixel. When the quantities of the red, green and blue lights are respectively generated by the red, green and blue sub-pixels, the quantities of the red, green and blue lights include in the white light have to be subtracted. In an example of RGB (0.6, 0.3, 0.3), a 0.3 of the quantity of the red light, a 0.3 of the quantity of the green light and a 0.3 of the quantity of the blue light are replaced by the white light. The 0.3 of the quantity of the red light is subtracted from the 0.6 of the quantity of the red light, the 0.3 of the quantity of the green light is subtracted from the 0.3 of the quantity of the green light and the 0.3 of the quantity of the blue light is subtracted from the 0.3 of the quantity of the blue light. Thus, RGB (0.6, 0.3, 0.3) is converted to RGBW (0.3, 0, 0, 0.3). However, since the sizes of the red, green and blue sub-pixels of RGBW are the ¾ of these of the RGB, a real converted brightness is RGBW (0.3*¾, 0, 0, 0.3*¾).